Characterization of Uranium in Bituminized Radioactive Waste Drums by Self-Induced X-Ray Fluorescence

Patrick Pin (1, 2) , Bertrand Perot (1, 2)

1 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)
2 LMN - Laboratoire de Mesures Nucléaires

This paper reports the experimental qualification of an original uranium characterization method based on fluorescence X rays induced by the spontaneous gamma emission of bituminized radioactive waste drums. The main 661.7 keV gamma ray following the $^{137}$Cs decay produces by Compton scattering in the bituminized matrix an intense photon continuum around 100 keV, i.e. in the uranium X-ray fluorescence region. “Self-induced” X-rays produced without using an external source allow a quantitative assessment of uranium as $^{137}$Cs and uranium are homogeneously mixed and distributed in the bituminized matrix. The paper presents the experimental qualification of the method with real waste drums, showing a detection limit well below 1 kg of uranium in 20 min acquisitions while the usual gamma rays of $^{235}$U (185.7 keV) or $^{238}$U (1001.0 keV of $^{234}$mPa in the radioactive decay chain) are not detected. The relative uncertainty on the uranium mass assessed by self-induced X-ray fluorescence (SXRF) is about 50%, with a 95% confidence level, taking into account the correction of photon attenuation in the waste matrix. This last indeed contains high atomic numbers elements like uranium, but also barium, in quantities which are not known for each drum. Attenuation is estimated using a peak-to-Compton ratio to limit the corresponding uncertainty. The SXRF uranium masses measured in the real drums are in good agreement with long gamma-ray spectroscopy measurements (1001.0 keV peak) or with radiochemical analyses

Mots clés: Bituminized radioactive waste; self-induced X-ray fluorescence; Atoms; Cesium; Gamma ray spectrometers; Gamma rays; Photons; Uncertainty analysis; Uranium; Bituminized radioactive wastes; Characterization methods; Gamma-ray spectroscopy; Photon attenuation; Quantitative assessments; Radiochemical analysis; Relative uncertainty; X ray fluorescence; Radioactive wastes

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

Patrick Pin, Bertrand Perot. Characterization of Uranium in Bituminized Radioactive Waste Drums by Self-Induced X-Ray Fluorescence. IEEE Transactions on Nuclear Science, 2014, 61 (4), pp.2131-2136. ⟨10.1109/TNS.2013.2283726⟩. ⟨cea-01992412⟩